MMP9 and breast cancer: To counter the inhibitory signals, tumor cells express high levels of anti-plasminogen activator serpins, including neuroserpin and serpin B2, to promote cancer cell survival and vascular co-option in brain metastasis.106 Co-cultured breast cancer cell lines with astrocytes exhibited astrocytes-derived factors MMP-2 and MMP-9, which induce both the migration and invasion of breast cancer cells.104 Microglia can also be activated by tumor cells and perform similar functions as astrocytes to promote colonization tumor cells, and this process occurs in a Wnt-dependent manner.107